Tire treads need to be provided with high levels of properties, such as mainly high fuel economy, high abrasion resistance and high wet grip performance, and various methods for improving these properties have been considered.
For example, fuel economy is known to be improved by introducing a functional group having an affinity for filler into the polymer chain end; abrasion resistance is known to be improved by using a high molecular weight polymer having a molecular weight of 250,000 or more; and wet grip performance is known to be improved by using a polymer having a high glass transition temperature (Tg).
However, the method of introducing a functional group having an affinity for filler, the method of using a high molecular weight polymer, and the method of using a polymer having a high Tg obtained by increasing the styrene content all lead to a problem of increasing the hardness of rubber compositions and deteriorating the processability.
Patent Literature 1 discloses a tire rubber composition having fuel economy, abrasion resistance, and wet grip performance that are improved by incorporation of a liquid resin having a softening point of −20° C. to 45° C. and a certain silica. However, there is still room for improvement in achieving a balanced improvement in these properties while providing good processability.